MEDUSA. 



161 



lower down the siphosome. The tentacles bud out from the sides of the 

 poly"pites, and then come the bracts which protect them. The units upon 

 the siphosome are separated by free internodes. When set free as Ersoea 

 appendiculata, each unit is provided with a covering scale, polypite, tentacle, 

 and immature swimming-bell. 



Ersaea appendiculata. 



Plate 9, fig. Ifi. 

 The mature animal is 5 mm. in length. The anterior covering scale 

 is irregularly pyramidal, one face being plane, with angular edges. The 

 ventral side is concave and fits over the anterior part of the swimming-bell. 

 The phyllocyst is long and is composed of highly vacuolated cells, and there 

 is generally an " oil globule " near its distal extremity. The swimming- 

 bell is quadratic in cross-section, having four longitudinal, sharp edges. 

 The cavity of the bell is quite wide at the base, but tapers to a narrow 

 inner apex. There is no manubrium, but there are four straight, narrow, 

 radial canals and a simple circular vessel. The velum is well developed, 

 and its contractions serve to drive the animal forward with considerable 

 speed. The single polypite is fusiform, and its entodermal gastric cells are 

 arranged in wart-like protuberances upon the inner wall of the stomach. 

 There is a single tentacle which gives rise to side branches, each one of 

 which terminates in a well developed nematocyst battery. Several gono- 

 phores in various stages of development arise from the side of the polypite 

 immediately proximal to the tentacle. Each gonophore contains four sim- 

 ple radial canals and a circular vessel. The entoderm of the polypite 

 is usually faint yellow, but occasionally it is of a delicate pink or milky 

 color. The radial canals of the swimming-bell are usually colorless, but 

 sometimes they are tinged with yellow spots. This form is common every- 



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